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Securely managed web applications

Azure App Service
Azure Application Gateway
Azure SQL Database
Azure VPN Gateway
Azure Web Application Firewall

This article provides an overview of deploying secure applications using the App Service Environment. To restrict application access from the internet, the Azure Application Gateway service and Azure Web Application Firewall are used. This article also provides guidance about continuous integration and continuous deployment (CI/CD) for App Service Environments using Azure DevOps.

This scenario is commonly deployed in industries such as banking and insurance, where customers are conscious of platform-level security in addition to application level security. To demonstrate these concepts, we'll use an application that allows users to submit expense reports.

Potential use cases

Consider this scenario for the following use cases:

  • Building an Azure Web App where extra security is required.
  • Providing dedicated tenancy, rather than shared tenant App Service Plans.
  • Using Azure DevOps with an internally load-balanced(ILB) Application Service Environment.

Architecture

Diagram featuring the sample scenario architecture for Secure ILB App Service Environment Deployment.

Download a Visio file of this architecture.

Dataflow

  1. HTTP/HTTPS requests first hit the application gateway.
  2. Optionally (not shown in the diagram), you can have Microsoft Entra authentication enabled for the Web App. After the traffic first hits the application gateway, the user would be prompted to supply credentials to authenticate with the application.
  3. User requests flow through the internal load balancer (ILB) of the environment, which in turn routes the traffic to the Expenses Web App.
  4. The user then proceeds to create an expense report.
  5. As part of creating the expense report, the deployed API App is invoked to retrieve the user's manager name and email.
  6. The created expense report is stored in Azure SQL Database.
  7. To facilitate continuous deployment, code is checked into the Azure DevOps instance.
  8. The build VM has the Azure DevOps Agent installed, allowing the build VM to pull the bits for the Web App to deploy to the App Service Environment (since the Build VM is deployed in a subnet inside the same virtual network).

Components

  • The App Service Environment provides a fully isolated, dedicated environment for securely running the application at high scale. In addition, because the App Service Environment and the workloads that run on it are behind a virtual network, it also provides an extra layer of security and isolation. The requirement of high scale and isolation drove the selection of ILB App Service Environment.
  • This workload uses the isolated App Service pricing tier, so the application runs in a private dedicated environment in an Azure datacenter using faster processors, solid-state drive (SSD) storage, and double the memory-to-core ratio compared to Standard.
  • Azure App Service Web App and API App host web applications and RESTful APIs. These apps and APIs are hosted on the Isolated service plan, which also offers autoscaling, custom domains, and so on, but in a dedicated tier.
  • Azure Application Gateway is a web traffic load balancer operating at Layer 7 that manages traffic to the web application. It offers SSL offloading, which removes extra overhead from the web servers hosting the web app to decrypt traffic again.
  • Web Application Firewall is a feature of Application Gateway. Enabling the web application firewall in the application gateway further enhances security. The web application firewall uses Open Worldwide Application Security Project (OWASP) rules to protect the web application against attacks such as cross-site scripting, session hijacks, and SQL injection.
  • Azure SQL Database was selected because most of the data in this application is relational data, with some data as documents and Blobs.
  • Azure Networking provides various networking capabilities in Azure, and the networks can be peered with other virtual networks in Azure. Connections can also be established with on-premises datacenters via ExpressRoute or site-to-site. In this case, a service endpoint is enabled on the virtual network to ensure the data is flowing only between the Azure virtual network and the SQL Database instance.
  • Azure DevOps is used to help teams collaborate during sprints, using features that support Agile Development, and to create build and release pipelines.
  • An Azure build VM was created so that the installed agent can pull down the respective build, and deploy the web app to the environment.

Alternatives

An App Service Environment can run regular web apps on Windows or, as in this example, web apps deployed inside the environment that are each running as Linux containers. An App Service Environment was selected to host these single-instance containerized applications. There are alternatives available—review the considerations below when designing your solution.

  • Azure Service Fabric: If your environment is mostly Windows-based, and your workloads are primarily .NET Framework-based, and you aren't considering rearchitecting to .NET Core, then use Service Fabric to support and deploy Windows Server Containers. Additionally, Service Fabric supports C# or Java programming APIs, and for developing native microservices, the clusters can be provisioned on Windows or Linux.
  • Azure Kubernetes Service (AKS) is an open-source project and an orchestration platform more suited to hosting complex multicontainer applications that typically use a microservices-based architecture. AKS is a managed Azure service that abstracts away the complexities of provisioning and configuring a Kubernetes cluster. However, significant knowledge of the Kubernetes platform is required to support and maintain it, so hosting a handful of single-instance containerized web applications might not be the best option.

Other options for the data tier include:

  • Azure Cosmos DB: If most of your data is in non-relational format, Azure Cosmos DB is a good alternative. This service provides a platform to run other data models such as MongoDB, Cassandra, Graph data, or simple table storage.

Considerations

There are certain considerations when dealing with certificates on ILB App Service Environment. You need to generate a certificate that is chained up to a trusted root without requiring a Certificate Signing Request generated by the server where the cert will eventually be stored. With Internet Information Services (IIS), for example, the first step is to generate a certificate signing request (CSR) from your IIS server and then send it to the SSL certificate-issuing authority.

You can't issue a CSR from the Internal load balancer (ILB) of an App Service Environment. The way to handle this limitation is to use the wildcard procedure.

The wildcard procedure allows you to use proof of DNS name ownership instead of a CSR. If you own a DNS namespace, you can put in special DNS TXT record, the wildcard procedure checks that the record is there, and if found, knows that you own the DNS server because you have the right record. Based on that information, it issues a certificate that is signed up to a trusted root, which you can then upload to your ILB. You don't need to do anything with the individual certificate stores on the Web Apps because you have a trusted root SSL certificate at the ILB.

Make self-signed or internally issued SSL cert work if you want to make secure calls between services running in an ILB App Service Environment. Another solution to consider on how to make ILB App Service Environment work with internally issued SSL certificate and how to load the internal CA to the trusted root store.

While provisioning the App Service Environment, consider the following limitations when choosing a domain name for the environment. Domain names can't be:

  • net
  • azurewebsites.net
  • p.azurewebsites.net
  • nameofthease.p.azurewebsites.net

Additionally, the custom domain name used for apps and the domain name used by the ILB App Service Environment can't overlap. For an ILB App Service Environment with the domain name contoso.com, you can't use custom domain names for your apps like:

  • www.contoso.com
  • abcd.def.contoso.com
  • abcd.contoso.com

Choose a domain for the ILB App Service Environment that won't conflict with those custom domain names. You can use something like contoso-internal.com for the domain of your environment for this example, because that won't conflict with custom domain names that end in .contoso.com.

Another point to consider is DNS. In order to allow applications within the App Service Environment to communicate with each other, for instance a web application to talk to an API, you'll need to have DNS configured for your virtual network holding the environment. You can either bring your own DNS or you can use Azure DNS private zones.

Availability

Scalability

Security

Resiliency

Deploy this scenario

To deploy this scenario, follow this step-by-step tutorial demonstrating how to manually deploy each component. Select App Service Environment v3 instead of v2, when following the tutorial. This tutorial also provides a .NET sample application that runs a simple Contoso expense reporting application.

Pricing

Explore the cost of running this scenario. All of the services are pre-configured in the cost calculator. To see how pricing would change for your particular use case, change the appropriate variables to match your expected traffic.

We've provided three sample cost profiles based on amount of traffic you expect to get:

  • Small: This pricing example represents the components necessary for a minimum production-level instance serving a few thousand users per month. The app is using a single instance of a standard web app that will be enough to enable autoscaling. Each of the other components is scaled to a Basic tier that will minimize cost but still ensure that there's service-level agreement (SLA) support and enough capacity to handle a production-level workload.
  • Medium: This pricing example represents the components needed for a moderate size deployment. Here we estimate approximately 100,000 users over the course of a month. The expected traffic is handled in a single App Service instance with a moderate Standard tier. Additionally, moderate tiers of cognitive and search services are added to the calculator.
  • Large: This pricing example represents an application meant for high scale, at the order of millions of users per month, moving terabytes of data. At this level of usage, high performance, Premium tier web apps deployed in multiple regions fronted by Traffic Manager are required. Data consists of the following components: storage, databases, and CDN, all configured for terabytes of data.

Contributors

This article is maintained by Microsoft. It was originally written by the following contributors.

Principal author:

  • Faisal Mustafa | Senior Customer Engineer

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